China announced Thursday it has begun building its second aircraft carrier, in the latest sign of Beijing's rapid modernization of its naval forces.

The carrier is being built "according to entirely domestic designs" in the northeastern port city of Dalian, Defense Ministry spokesman Yang Yujun said.

China's only other carrier, the Liaoning, was purchased from Ukraine in 1998. It underwent extensive retrofitting in China before going into service in 2012.

Yang said China's experience refurbishing the Liaoning "led to many areas of improvement and enhancements" for the new carrier, which will be about the same size as the older vessel.

The new 50,000-ton carrier will use conventional rather than nuclear power, Yang said. It will carry China's J-15 fighter jets and other aircraft that will employ a ski-jump takeoff.

No launch date yet

Yang said the launch date for the so-far-unnamed vessel is not clear and depends on progress made in the design process. He also would not comment on whether China planned to build additional carriers.

The announcement follows months of rumors and news reports that China was planning to build its first-ever domestically designed aircraft carrier, despite the concerns of many of its neighbors.

China is engaged in tense territorial disputes with many Asian countries, particularly in the vast South China Sea, which Beijing claims almost in its entirety.

Beijing has stressed that the expansion of its navy is no threat to its neighbors. It has said the Liaoning will be used mainly for scientific research and training missions.

The Liaoning is not yet fully functional. But it has already conducted South China Sea training missions that suggest Beijing will continue to take an assertive stance on the maritime disputes.